1. Field of the Invention
The present invention relates to a brass alloy and more particularly, to a lead-free brass alloy including less than 0.25 wt % of lead.
2. Description of Related Art
A brass includes copper and zinc, as major ingredients, usually in a ratio of about 7:3 or 6:4. In addition, a brass usually includes a small amount of impurities. In order to improve the properties of a brass, a conventional brass contains lead (mostly in the range of 1 to 3 wt %) to achieve the desired mechanical properties for use in the industry, thereby becoming an important industrial material that is widely applicable to metallic devices and valves for use in pipelines, faucets and water supply and discharge systems.
However, as awareness of the importance of environmental protection increases and the impact of heavy metals on human health becomes better understood, it is a trend to restrict the use of lead-containing alloys. Japan and the United States, have progressively amended relevant regulations in an intensive effort to lower the lead content in the environment by particularly requiring that no lead shall leach from lead-containing alloys used in products ranging from household appliances and automobiles to residential water pipes and municipal water systems, while also requiring that lead contamination shall be avoided during processing.
On the other hand, if the zinc content of brass exceeds 20 wt %, corrosion (such as dezincification) is likely to occur. Since dezincification seriously damages the structure of brass, the surface integrity of brass products is lowered and even pores may be formed in brass pipes. This significantly decreases the lifespan of brass products, thereby causing application problems.
In order to overcome the aforesaid high content of lead and dezincification, it is a trend to develop novel copper alloy formulations. For example, Taiwanese Patent No. 421674, U.S. Pat. No. 7,354,489, and US Patent Application Publication Nos. 20070062615, 20060078458, 2004023441 and 2002069942 disclose adding silicon (Si) and other elements to form lead-free copper alloys. However, the alloys made from these formulations have poor property for cutting. Chinese Patent Application Publication No. 10144045 discloses aluminum, silicon and phosphorous as main components of a lead-free copper alloy. This lead-free copper alloy can be used for casting, but has poor property for cutting and much lower processing efficiency than lead-containing brass. Chinese Patent Application Publication Nos. 101285138 and 101285137 disclose phosphorous-containing lead-free copper alloy; however, cracks are easily formed while casting this alloy.
In addition, U.S. Pat. Nos. 7,297,215, 6,974,509, 6,955,378, 6,149,739, 5,942,056, 5,637,160, 5,653,827, 5,487,867 and 5,330,712, and US Patent Application Publication Nos. 20060005901, 20040094243 and 20070039667 disclose lead-free or low-lead bismuth-containing brass alloy formulations, wherein the bismuth content of the formulations ranges from 0.5 wt % to 7 wt %; however, the high content of bismuth in the alloy causes cracks on the surface of the cast. Further, Chinese Patent Application Publication No. 101403056 discloses a lead-free brass alloy containing bismuth and manganese, but this alloy still has the drawbacks owing to the high content of bismuth. If the bismuth content is decreased and the manganese content is increased, the stiffness would be enhanced but the cutting property would be poor. Chinese Patent Application Publication No. 101440445 discloses an aluminum brass alloy having bismuth and zinc, wherein tin is also included for improving cutting property of the aluminum brass alloy; however, this alloy is not so applicable for subsequent processing owing to its hardness.
Therefore, there is a need to develop a formulation for forming an alloy having better corrosion resistance, casting property, cutting property and mechanical property.